The linear perfluorohydrocarbon polymer—polytetrafluoroethylene (PTFE)—is one of the most hydrophobic and oleophobic materials known and has excellent thermal and chemical stability. [For example, see “Chemistry of Organic Fluorine Compounds II: A Critical Review” (ACS Monograph, ISSN 0065-7719; 187), edited by Milo{hacek over (s)} Hudlický/and Attlila E. Pavlath, 1995; and “Organofluorine Chemistry: Principle and Commercial Applications” edited by R. E. Banks, B. E. Smart, and J. C. Tatlow, 1994.] However, one disadvantage of PTFE is that it cold flows under elevated pressure and/or temperature which has limited its use in some applications, e.g., in the coating of bearings. [See U.S. Pat. Nos. 4,237,376 and 4,618,734.]
Additional disadvantages of PTFE are: a very high melting point of the crystalline CF2CF2 chains that make it difficult to process; and its lack of solubility in commonly used solvents which limits its application as a solution-born coating material. Also, PTFE cannot be used for liquid-based applications such as a lubricating fluid or as a base oil for greases.
These adverse effects which result from PTFE's crystalline nature have been alleviated by: a) reducing the crystallinity by copolymerization with other entities, or b) replacing some of the fluorine atoms in the C2F2 chain(s) with other groups. Examples of such copolymers are fluorinated ethylene propylene resins (FEP), perfluoroalkoxy resins (PFA), poly(chlorotrifluoroethylene)s (PCTFE), perfluorocarbon ethers and similar copolymers. However, incorporation of other entities to form copolymers often adversely affects thermal properties, chemical stability and the surface energy of the resulting materials to varying, and unpredictable degrees. For example, the incorporation of polar groups such as ethers, esters, amides or chlorine will reduce the hydrophobicity and oleophobicity of the copolymers. [For example, see “Chemistry of Organic Fluorine Compounds II: A Critical Review” (ACS Monograph, ISSN 0065-7719; 187), edited by Milo{hacek over (s)} Hudlický and Attila E. Pavlath, 1995; and “Organofluorine Chemistry: Principle and Commercial Applications” edited by R. E. Banks, B. E. Smart, and J. C. Tatlow, 1994.] Copolymers that retain the CF2 backbone can retain some or most of the desirable properties of PTFE while improving other properties such as processibility, solubility, low Tg and the ability to be crosslinked. Such a combination of properties makes these materials very interesting and provides many applications. Known copolymers that contain a CF2 backbone have been limited to linear polymers or to crosslined networks. [See U.S. Pat. Nos. 4,237,376 and 4,618,734.]
Hydrophobic and oleophobic fluorocarbon networks made from small molecular fluorocarbons have been described, e.g., networks from perfluoroalkylene acetylene compounds. [See U.S. Pat. Nos. 4,237,376 and 4,618,734.] These compounds prior to curing are not polymers and are volatile in high-temperature curing. Also, the viscosities of their formulations are not readily adjustable.
Some curable linear fluorocarbon network-forming copolymers include the DuPont Fluoropolymer B (65% vinylidene fluoride, 25% tetrafluoroethylene and 10% vinylbutyrate), the Abcite® and Lucite® fluoropolymers (based on crosslinked mixtures of hydroxyl-fluoropolymers) and Lumiflon® fluoropolymer (a copolymer of tetrafluoroethlene with a monomer having hydrophilic side groups). These fluorocarbon network-forming polymers generally contain polar groups.
Networks of hydrophobic hyperbranched polymers that contain silicon entities such as polycarbosiloxanes have been described [see U.S. Pat. Nos. 6,384,172 and 6,646,089], but networks of hyperbranched perfluorocarbon polymers have not been reported.